console.clear();

var MAX_LIFE = 50;
var canvas = document.querySelector('canvas');
var input = document.querySelector('input');
var field = {}
var hasFocus = false;
var caret = document.createElement('span');
caret.style.cssText = document.defaultView.getComputedStyle(input, '').cssText;
caret.style.position = 'absolute';
caret.style.left = 0;
caret.style.top = 0;
caret.style.width = 'auto';
caret.style.visibility = 'hidden';
document.body.appendChild(caret);

function reposition() {
    field = input.getBoundingClientRect();
}
window.onload = reposition;
window.onresize = reposition;
reposition();

input.onfocus = function () {
    hasFocus = true
}
input.onblur = function () {
    hasFocus = false
}

function rain() {

}

function burst(intensity) {

    var behavior = [
        this.behavior.cohesion(),
        this.behavior.move()
    ];

    var size = .75;
    var force = .7;
    var lifeMin = 0;
    var progress = Math.min(field.width, caret.offsetWidth) / field.width;
    var offset = field.left + (field.width * progress);
    var rangeMin = Math.max(field.left, offset - 30);
    var rangeMax = Math.min(field.right, offset + 10);

    this.spray(intensity, function () {
        return [
            null, null,
            Vector.create(
                Random.between(rangeMin + 10, rangeMax - 20),
                Random.between(field.top + 15, field.bottom - 15)
            ),
            Vector.random(force),
            size + Math.random(),
            Random.between(lifeMin, 0), behavior
        ]
    });

    // top edge
    this.spray(intensity * .5, function () {
        return [
            null, null,
            Vector.create(
                Random.between(rangeMin, rangeMax),
                field.top
            ),
            Vector.random(force),
            size + Math.random(),
            Random.between(lifeMin, 0), behavior
        ]
    });

    // bottom edge
    this.spray(intensity * .5, function () {
        return [
            null, null,
            Vector.create(
                Random.between(rangeMin, rangeMax),
                field.top + field.height
            ),
            Vector.random(force),
            size + Math.random(),
            Random.between(lifeMin, 0), behavior
        ]
    });

    // left edge
    if (input.value.length === 1) {

        this.spray(intensity * 2, function () {
            return [
                null, null,
                Vector.create(
                    field.left,
                    Random.between(field.top, field.bottom)
                ),
                Vector.random(force),
                size + Math.random(),
                Random.between(lifeMin, 0), behavior
            ]
        });
    }

    // right edge
    if (rangeMax == field.right) {

        this.spray(intensity * 2, function () {
            return [
                null, null,
                Vector.create(
                    field.right,
                    Random.between(field.top, field.bottom)
                ),
                Vector.random(force),
                size + Math.random(),
                Random.between(lifeMin, 0), behavior
            ]
        });

    }

}

// start particle simulation
simulate(
    '2d', {
        init: function () {

        },
        tick: function (particles) {

            if (!particles) {
                return;
            }

            particles.forEach(function (p) {

                if (p.life > MAX_LIFE) {
                    this.destroy(p);
                }

            });

        },
        beforePaint: function () {
            this.clear();
        },
        paint: function (particle) {

            var p = particle.position;
            var s = particle.size;
            var o = 1 - (particle.life / MAX_LIFE);

            this.paint.circle(p.x, p.y, s, 'rgba(255,255,255,' + o + ')');
            this.paint.circle(p.x, p.y, s + 2, 'rgba(231,244,255,' + (o * .25) + ')');

        },
        afterPaint: function () {
            // nothing
        },
        action: function (x, y) {

            caret.textContent = input.value;

            burst.call(this, 10);

            input.classList.add('keyup');
            setTimeout(function () {
                input.classList.remove('keyup')
            }, 100);

        }
    }
);

// "simulate" particle simulation logic
/**
 * Constants
 */
PI_2 = Math.PI / 2;
PI_180 = Math.PI / 180;

/**
 * Random
 */
var Random = {
    between: function (min, max) {
        return min + (Math.random() * (max - min));
    }
}

/**
 * 2D Vector Class
 */
function Vector(x, y) {
    this._x = x || 0;
    this._y = y || 0;
}

Vector.create = function (x, y) {
    return new Vector(x, y);
};

Vector.add = function (a, b) {
    return new Vector(a.x + b.x, a.y + b.y);
};

Vector.subtract = function (a, b) {
    return new Vector(a.x - b.x, a.y - b.y);
};

Vector.random = function (range) {
    var v = new Vector();
    v.randomize(range);
    return v;
};

Vector.distanceSquared = function (a, b) {
    var dx = a.x - b.x;
    var dy = a.y - b.y;
    return dx * dx + dy * dy;
};

Vector.distance = function (a, b) {
    var dx = a.x - b.x;
    var dy = a.y - b.y;
    return Math.sqrt(dx * dx + dy * dy);
};

Vector.prototype = {
    get x() {
        return this._x;
    },
    get y() {
        return this._y;
    },
    set x(value) {
        this._x = value;
    },
    set y(value) {
        this._y = value;
    },
    get magnitudeSquared() {
        return this._x * this._x + this._y * this._y;
    },
    get magnitude() {
        return Math.sqrt(this.magnitudeSquared);
    },
    get angle() {
        return Math.atan2(this._y, this._x) * 180 / Math.PI;
    },
    clone: function () {
        return new Vector(this._x, this._y);
    },
    add: function (v) {
        this._x += v.x;
        this._y += v.y;
    },
    subtract: function (v) {
        this._x -= v.x;
        this._y -= v.y;
    },
    multiply: function (value) {
        this._x *= value;
        this._y *= value;
    },
    divide: function (value) {
        this._x /= value;
        this._y /= value;
    },
    normalize: function () {
        var magnitude = this.magnitude;
        if (magnitude > 0) {
            this.divide(magnitude);
        }
    },
    limit: function (treshold) {
        if (this.magnitude > treshold) {
            this.normalize();
            this.multiply(treshold);
        }
    },
    randomize: function (amount) {
        amount = amount || 1;
        this._x = amount * 2 * (-.5 + Math.random());
        this._y = amount * 2 * (-.5 + Math.random());
    },
    rotate: function (degrees) {
        var magnitude = this.magnitude;
        var angle = ((Math.atan2(this._x, this._y) * PI_HALF) + degrees) * PI_180;
        this._x = magnitude * Math.cos(angle);
        this._y = magnitude * Math.sin(angle);
    },
    flip: function () {
        var temp = this._y;
        this._y = this._x;
        this._x = temp;
    },
    invert: function () {
        this._x = -this._x;
        this._y = -this._y;
    },
    toString: function () {
        return this._x + ', ' + this._y;
    }
}

/**
 * Particle Class
 */
function Particle(id, group, position, velocity, size, life, behavior) {

    this._id = id || 'default';
    this._group = group || 'default';

    this._position = position || new Vector();
    this._velocity = velocity || new Vector();
    this._size = size || 1;
    this._life = Math.round(life || 0);

    this._behavior = behavior || [];

}

Particle.prototype = {
    get id() {
        return this._id;
    },
    get group() {
        return this._group;
    },
    get life() {
        return this._life;
    },
    get size() {
        return this._size;
    },
    set size(size) {
        this._size = size;
    },
    get position() {
        return this._position;
    },
    get velocity() {
        return this._velocity;
    },
    update: function (stage) {

        this._life++;

        var i = 0;
        var l = this._behavior.length;

        for (; i < l; i++) {
            this._behavior[i].call(stage, this);
        }

    },
    toString: function () {
        return 'Particle(' + this._id + ') ' + this._life + ' pos: ' + this._position + ' vec: ' + this._velocity;
    }
}

// setup DOM
function simulate(dimensions, options) {

    // private vars
    var particles = [];
    var destroyed = [];
    var update = update || function () {
        };
    var stage = stage || function () {
        };
    var canvas;
    var context;

    if (!options) {
        console.error('"options" object must be defined');
        return;
    }

    if (!options.init) {
        console.error('"init" function must be defined');
        return;
    }

    if (!options.paint) {
        console.error('"paint" function must be defined');
        return;
    }

    if (!options.tick) {
        options.tick = function () {
        };
    }

    if (!options.beforePaint) {
        options.beforePaint = function () {
        };
    }

    if (!options.afterPaint) {
        options.afterPaint = function () {
        };
    }

    if (!options.action) {
        options.action = function () {
        };
    }

    if (document.readyState === 'interactive') {
        setup();
    } else {
        document.addEventListener('DOMContentLoaded', setup);
    }

    // resizes canvas to fit window dimensions
    function fitCanvas() {
        canvas.width = window.innerWidth;
        canvas.height = window.innerHeight;
    }

    // create canvas for drawing
    function setup() {

        // create
        canvas = document.createElement('canvas');
        document.body.appendChild(canvas);

        // correct canvas size on window resize
        window.addEventListener('resize', fitCanvas);

        // go
        go();
    }

    // canvas has been attached, let's go!
    function go() {

        // set initial canvas size
        fitCanvas();

        // get context for drawing
        context = canvas.getContext(dimensions);

        // simulation update loop
        function act() {

            // update particle states
            var i = 0;
            var l = particles.length;
            var p;
            for (; i < l; i++) {
                particles[i].update(this);
            }

            // clean destroyed particles
            while (p = destroyed.pop()) {

                do {

                    // has not been found in destroyed array?
                    if (p !== particles[i]) {
                        continue;
                    }

                    // remove particle
                    particles.splice(i, 1);

                } while (i-- >= 0)
            }

            // repaint context
            options.beforePaint.call(this);

            // repaint particles
            i = 0;
            l = particles.length;
            for (; i < l; i++) {
                options.paint.call(this, particles[i]);
            }

            // after particles have been painted
            options.afterPaint.call(this);
        }

        function tick() {

            // call update method, this allows for inserting particles later on
            options.tick.call(this, particles);

            // update particles here
            act();

            // on to the next frame
            window.requestAnimationFrame(tick);

        }

        /**
         * API
         **/
        function clear() {
            context.clearRect(0, 0, canvas.width, canvas.height);
        }

        function destroy(particle) {
            destroyed.push(particle);
        }

        function add(id, group, position, velocity, size, life, behavior) {
            particles.push(new Particle(id, group, position, velocity, size, life, behavior));
        }

        function spray(amount, config) {
            var i = 0;
            for (; i < amount; i++) {
                add.apply(this, config());
            }
        }

        function debug(particle) {
            this.paint.circle(
                particle.position.x,
                particle.position.y,
                particle.size,
                'rgba(255,0,0,.75)'
            );
            context.beginPath();
            context.moveTo(particle.position.x, particle.position.y);
            context.lineTo(particle.position.x + (particle.velocity.x * 10), particle.position.y + (particle.velocity.y * 10));
            context.strokeStyle = 'rgba(255,0,0,.1)';
            context.stroke();
            context.closePath();
        };

        this.clear = clear;
        this.destroy = destroy;
        this.add = add;
        this.spray = spray;
        this.debug = debug;

        this.paint = {
            circle: function (x, y, size, color) {
                context.beginPath();
                context.arc(x, y, size, 0, 2 * Math.PI, false);
                context.fillStyle = color;
                context.fill();
            },
            square: function (x, y, size, color) {
                context.beginPath();
                context.rect(x - (size * .5), y - (size * .5), size, size);
                context.fillStyle = color;
                context.fill();
            }
        }

        this.behavior = {
            cohesion: function (range, speed) {
                range = Math.pow(range || 100, 2);
                speed = speed || .001;
                return function (particle) {

                    var center = new Vector();
                    var i = 0;
                    var l = particles.length;
                    var count = 0;

                    if (l <= 1) {
                        return;
                    }

                    for (; i < l; i++) {

                        // don't use self in group
                        if (particles[i] === particle || Vector.distanceSquared(particles[i].position, particle.position) > range) {
                            continue;
                        }

                        center.add(Vector.subtract(particles[i].position, particle.position));
                        count++;
                    }

                    if (count > 0) {

                        center.divide(count);

                        center.normalize();
                        center.multiply(particle.velocity.magnitude);

                        center.multiply(.05);
                    }

                    particle.velocity.add(center);

                }
            },
            separation: function (distance) {

                var distance = Math.pow(distance || 25, 2);

                return function (particle) {

                    var heading = new Vector();
                    var i = 0;
                    var l = particles.length;
                    var count = 0;
                    var diff;

                    if (l <= 1) {
                        return;
                    }

                    for (; i < l; i++) {

                        // don't use self in group
                        if (particles[i] === particle || Vector.distanceSquared(particles[i].position, particle.position) > distance) {
                            continue;
                        }

                        // stay away from neighbours
                        diff = Vector.subtract(particle.position, particles[i].position);
                        diff.normalize();

                        heading.add(diff);
                        count++;
                    }

                    if (count > 0) {

                        // get average
                        heading.divide(count);

                        // make same length as current velocity (so particle won't speed up)
                        heading.normalize();
                        heading.multiply(particle.velocity.magnitude);

                        // limit force to make particle movement smoother
                        heading.limit(.1);
                    }

                    particle.velocity.add(heading);

                }
            },
            alignment: function (range) {
                range = Math.pow(range || 100, 2);
                return function (particle) {

                    var i = 0;
                    var l = particles.length;
                    var count = 0;
                    var heading = new Vector();

                    if (l <= 1) {
                        return;
                    }

                    for (; i < l; i++) {

                        // don't use self in group also don't align when out of range
                        if (particles[i] === particle || Vector.distanceSquared(particles[i].position, particle.position) > range) {
                            continue;
                        }

                        heading.add(particles[i].velocity);
                        count++;
                    }

                    if (count > 0) {

                        heading.divide(count);
                        heading.normalize();
                        heading.multiply(particle.velocity.magnitude);

                        // limit
                        heading.multiply(.1);

                    }

                    particle.velocity.add(heading);

                }
            },
            move: function () {
                return function (particle) {
                    particle.position.add(particle.velocity);

                    // handle collisions?

                }
            },
            eat: function (food) {
                food = food || [];
                return function (particle) {

                    var i = 0;
                    var l = particles.length;
                    var prey;

                    for (; i < l; i++) {

                        prey = particles[i];

                        // can't eat itself, also, needs to be tasty
                        if (prey === particle || food.indexOf(prey.group) === -1) {
                            continue;
                        }

                        // calculate force vector
                        if (Vector.distanceSquared(particle.position, neighbour.position) < 2 && particle.size >= neighbour.size) {
                            particle.size += neighbour.size;
                            destroy(neighbour);
                        }

                    }
                }
            },
            force: function (x, y) {
                return function (particle) {
                    particle.velocity.x += x;
                    particle.velocity.y += y;
                }
            },
            limit: function (treshold) {
                return function (particle) {
                    particle.velocity.limit(treshold);
                }
            },
            attract: function (forceMultiplier, groups) {
                forceMultiplier = forceMultiplier || 1;
                groups = groups || [];
                return function (particle) {

                    // attract other particles
                    var totalForce = new Vector(0, 0);
                    var force = new Vector(0, 0);
                    var i = 0;
                    var l = particles.length;
                    var distance;
                    var pull;
                    var attractor;
                    var grouping = groups.length;

                    for (; i < l; i++) {

                        attractor = particles[i];

                        // can't be attracted by itself or mismatched groups
                        if (attractor === particle || (grouping && groups.indexOf(attractor.group) === -1)) {
                            continue;
                        }

                        // calculate force vector
                        force.x = attractor.position.x - particle.position.x;
                        force.y = attractor.position.y - particle.position.y;
                        distance = force.magnitude;
                        force.normalize();

                        // the bigger the attractor the more force
                        force.multiply(attractor.size / distance);

                        totalForce.add(force);
                    }

                    totalForce.multiply(forceMultiplier);

                    particle.velocity.add(totalForce);
                }
            },
            wrap: function (margin) {
                return function (particle) {

                    // move around when particle reaches edge of screen
                    var position = particle.position;
                    var radius = particle.size * .5;

                    if (position.x + radius > canvas.width + margin) {
                        position.x = radius;
                    }

                    if (position.y + radius > canvas.height + margin) {
                        position.y = radius;
                    }

                    if (position.x - radius < -margin) {
                        position.x = canvas.width - radius;
                    }

                    if (position.y - radius < -margin) {
                        position.y = canvas.height - radius;
                    }

                }
            },
            reflect: function () {

                return function (particle) {

                    // bounce from edges
                    var position = particle.position;
                    var velocity = particle.velocity;
                    var radius = particle.size * .5;

                    if (position.x + radius > canvas.width) {
                        velocity.x = -velocity.x;
                    }

                    if (position.y + radius > canvas.height) {
                        velocity.y = -velocity.y;
                    }

                    if (position.x - radius < 0) {
                        velocity.x = -velocity.x;
                    }

                    if (position.y - radius < 0) {
                        velocity.y = -velocity.y;
                    }
                }

            },
            edge: function (action) {
                return function (particle) {

                    var position = particle.position;
                    var velocity = particle.velocity;
                    var radius = particle.size * .5;

                    if (position.x + radius > canvas.width) {
                        action(particle);
                    }

                    if (position.y + radius > canvas.height) {
                        action(particle);
                    }

                    if (position.x - radius < 0) {
                        action(particle);
                    }

                    if (position.y - radius < 0) {
                        action(particle);
                    }
                }
            }
        }

        // public
        Object.defineProperties(this, {
            'particles': {
                get: function () {
                    return particles;
                }
            },
            'width': {
                get: function () {
                    return canvas.width;
                }
            },
            'height': {
                get: function () {
                    return canvas.height;
                }
            },
            'context': {
                get: function () {
                    return context;
                }
            }
        });

        // call init method so the scene can be setup
        options.init.call(this)

        // start ticking
        tick();

        // start listening to events
        var self = this;
        document.addEventListener('keyup', function (e) {
            options.action.call(self, e.pageX, e.pageY);
        });

    }

};